A document scanner is a device that optically scans images, text and the like from documents and other media and converts it to a digital image that can be replicated. Duplex document scanning is an important feature of imaging devices. Duplex document scanning involves scanning both sides of a media as opposed to simplex scanning where only one side of the media is scanned.
Generally, there are two types of duplex document scanning systems. The first type uses a recirculating media feed path and a single scan head assembly. The single scan head assembly is shared by both a flatbed scanner and an automatic document feeder (ADF). A flatbed scanner is usually composed of a transparent flat platen, which is used to receive the media being scanned. Under the platen is a light source, such as a xenon lamp, to illuminate the media being scanned. Further, the flatbed scanner has mirrors to direct reflected light from the media to an image sensor, such as a charge-coupled device (CCD) module to capture the image via a lens to focus the light.
The second type of duplex document scanning system uses a direct single pass media feed path with two scan head assemblies located on each side of the media feed path. In this arrangement, a first scan head assembly is shared by the flatbed scanner and the ADF for scanning the top or “face-up” side of the media. The first scan head assembly typically located below the media feed path is similar to the single scan head assembly discussed above for the flatbed scanner. A second scan head assembly typically located above the media feed path is used for scanning the bottom or “backside” of the media. The second scan head assembly or “backside” scan head assembly has similar components as the first scan head assembly, such as a light source, mirror, CCD module and lens. Instead of having a platen at a top surface of the scan head assembly, a transparent plate made of glass or other similar rigid material is located at a bottom part of the second scan head assembly. Due to this arrangement, a top face of the transparent plate collects contamination particles as a result of gravity forcing particles downward. Since the transparent plate is close to the document plane, any blocking of the optical path by contamination particles to the media surface causes false vertical lines in the scanned image either in black or in color depending on where the contamination particles are relative to the sensor arrays.
In practice, it is nearly impossible to prevent contamination particles from accumulating in the second scan head assembly. Even if the second scan head assembly was assembled under ideal conditions, aging and vibration creates contamination particles. Further, the media travels along the media feed path through the ADF, and it is difficult to prevent contamination particles, such as dust from entering the second scan head assembly. As a result, the top face of the transparent plate is often contaminated.
In addition, the transparent plate sometimes serves as a sealing component of a portion of a bottom part of the second scan head assembly. The positioning of the transparent plate is critical to the function of the second scan head assembly. Specifically, if the distance between the transparent plate and the CCD module in the second scan head assembly is varied, the quality of the scan of the media may be decreased, such as being out of focus. Accordingly, the transparent plate is typically designed and assembled in a manner that it cannot be detached by an operator.
Since the transparent plate cannot be detached by the operator, the operator cannot clean and eliminate the contamination particles on the top face of the transparent plate because it is inaccessible. In contrast, the bottom face of the transparent plate (and the platen of the first scan head) are not sealed and are easily accessible by the operator for cleaning purposes. The only way to remedy the contamination problem is to contact the manufacture of the imaging device to purchase a new replacement scan head assembly. Each time a scan head assembly is replaced, there are typically registration and alignment procedures that must be completed before the new assembly will function correctly. As a result, it is costly and time consuming to replace the scan head assembly.
Accordingly, the art of imaging devices has a need for allowing operators access to the top face of the transparent plate of the scan head assembly located above a media feed path for cleaning contamination particles in a cost-effective and timely manner while allowing operators to easily reattach the transparent plate to the scan head assembly without effecting optical position precision.